[en] In determining the filter velocity of an undisturbed ground-water flow, summarized, the following information is necessary: 1) Information about the measuring device. a) Shape and position of the measuring probe within the diluting volume: radius and height of the measuring probe height of the diluting volume; b) Type of the measuring probe: resolution resp. dead time; c) Length of the packings bounding the diluting volume. 2) Information about the boring and its construction. a) Borehole radius; b) Well-filter tube: type of filter tube, nominal width and slot width; c) Filtering sand resp. gravel: origin and range of grain sites (resp. about 2 l sample). 3) Information about the ground-water conductor. Stratum inventory and information about the range of grain sites (resp. 10 l sample). 4) Information about the applied tracer type of the gamma tracer (half life) and chemical concentration. (orig./HP)